The present invention relates generally to mechanical presses and in particular to a shutheight adjustment mechanism, wherein punching and snapthrough loads through the shutheight adjustment mechanism are more accurately controlled.
Mechanical presses, for example, stamping presses and drawing presses, comprise a frame having a crown and bed and a slide supported within the frame for motion toward and away from the bed. The slide is driven by a crankshaft having a connecting arm connected to the slide. Such mechanical presses are widely used for stamping and drawing operations and vary substantially in size and available tonnage depending upon the intended use.
In prior art presses of this type, the slide is generally connected to the crankshaft by a connecting rod which is adjustable in length or which is connected to another member, such as a connection screw that is adjustable in its relation to the slide so that the shutheight opening between the slide and the bed can be adjusted to accommodate various die sets. Alternatively, the bed portion or bolster of the press may have its position adjusted relative to the slide so as to adjust the shutheight therebetween, as disclosed in U.S. Pat. No. 3,858,432. Regardless of the mode of shutheight adjustment, the slide is generally guided on the uprights of the press frame extending between the crown and the bed so that the parts of the die set remain in accurate registration as the slide reciprocates.
Many prior art mechanical presses include a plurality of adjustment screw assemblies within a shutheight adjustment mechanism attached to the bolster, whereby the position of the bolster is adjusted simultaneously by each of the adjustment screws. Bolster position may be changed by means of an interconnected worm and worm gear arrangement rotating the adjustment screws. The worm and worm gear are driven either manually or by means of a motor.
Prior problems with shutheight adjustment mechanisms include the transfer of punching and rebound loads through the adjustment mechanisms and adjustment screws during press operation. A press load is the load created by the mechanical press when the slide is urging its associated die into contact with the work piece. When the work piece fractures in the die, the slide attempts to rapidly accelerate downward, i.e. snapthrough. This snapthrough load is comprised mainly of this downward acceleration and the downward slider crank inertial acceleration of the die and slide combination. At the same time, the bolster accelerates in an upward direction, i.e. rebound. These loads, if not compensated for, cause changes in shutheight during press operation.
A particular problem for accurately controlling press shutheight is the tolerances between the connected portions of the press, and specifically the connections of the shutheight adjustment mechanism to the bolster. Shutheight adjustment mechanisms require certain clearances between the parts during manufacture, assembly, and adjustment so that the worm gear, adjustment nuts, and connection screws may turn and operate. These same clearances between the parts cause a problem during press use, since the clearances increase the possible ranges of shutheight.
The clearances within the shutheight adjustment mechanism also prevent the even transmission of pressure loads through the press. This uneven transmission of forces may cause particular parts, undergoing concentrated impact forces, to fail. Again, the clearances between the parts permit the shutheight to variably change during operation of the press, resulting in workpieces that may not meet design specifications.
The present invention is directed to overcome the aforementioned problems associated with mechanical press shutheight adjustment mechanisms wherein it is desired to accurately control shutheight while increasing protection of the shutheight adjustment mechanism by preloading and stabilizing the shutheight adjustment screw.